Brake linkages of this type are known from British Pat. No. 845,806 in the form of a brake power motor and auxiliary motor formed as separate pressure air cylinders, but are suitable only for a block brake unit of rail vehicles. A similar structure is known from German Pat. No. 23 46 828, in this case with a common pressure air cylinder for both the brake power motor and the auxiliary motor, and suited for brake clamps for rail vehicle disc brakes as well as for block brake units.
In the British patent, clamping of the vehicle friction brake is achieved with the aid of an eccentric drive movable by the pressure air cylinder serving as brake power motor, the bearing location of this drive being adjustable by the vent play regulator. The latter is provided with a screw drive with a threaded spindle and a nut threaded thereon, this screw drive being screwable on a ratchet drive serving as a one-way coupling. The pressure air cylinder serving as brake power motor is directly loaded with pressurized air corresponding in pressure to the desired degree of braking.
If the piston of this pressure air cylinder passes a certain distance of travel during braking, it then slides past an opening leading to the inlet chamber of the pressure air cylinder serving as auxiliary motor, so that the latter, too, is now impacted by the brake pressure air, is displaced during idling against spring force, and upon succeeding brake pressure air reduction during brake release causes adjustment of the vent play of the friction brake.
In the case of this brake linkage, the large cross-sectioned pressure air cylinder serving as brake power motor must carry out a stroke via translation of the brake linkage which causes both brake venting and brake clamping. The stroke is thus relatively large, so that this brake cylinder must be of large size, requires a corresponding structural volume and, during braking, a corresponding large, non-recoverable amount of pressurized air, i.e., amount of energy, for clamping of the friction brake. Moreover, this prior art structure provides for only an incremental adjustment of the stroke of the vent play of the friction brake, dependent on the stroke of the brake power pressure air cylinder, so that, upon alteration of the brake linkage translation ratio, often required in order to adapt the brake linkage to the vehicle to be equipped, the position of the channel openings in the cylinder must also be altered, so that a different kind of this type of pressurized air cylinder is needed.
In German Pat. No. 23 46 828, a pressure air cylinder dimensioned as a brake power motor is arranged between the ends of two brake clamps/brake levers, and the distance between these ends is scanned by a Bowden cable and is transmitted via a stop device as drive for a ratchet drive for a threaded spindle, which serves as pull rod for the brake clamp. Two nuts are threaded on oppositely threaded portions of this spindle, these being articulated on the central regions of the two brake clamps/brake levers. Here, too, the large pressure air cylinder must effectuate both the vent play as well as the clamping stroke for the disc brake, only incremental adjustment is possible, and the particular translational ratio of the brake clamp influences the adjustment control.
Thus, in the brake linkages of the two described prior art devices, rapid and energy efficient application of the vehicle friction brake does not occur prior to activation of the brake power motor.
For the purpose of such rapid and energy efficient brake application, it is known from German No. 24 650 to provide a bell crank linkage extensible by means of an auxiliary motor in the brake linkage movable by means of the brake power motor; no vent play regulator is provided at all. The effect of the bell crank linkage is influenced by the translational ratio of the brake linkage, so that it must be dimensioned in accordance with the particular brake linkage translational ratio in question. While a vent play regulator could be incorporated into this brake linkage, this would greatly increase the constructional requirements.
From German Nos. 937 291 and 1 200 343, brake linkages are known which are movable by a brake power motor and which have threaded drives switchable by couplings, and which can switch over the brake linkage from a low translation effecting rapid brake application to a high one effecting large brake clamping force, in dependency on the tension level in the brake linkage or constructively determined brake power motor strokes. However, these brake linkages have a rather complex structure including several threaded spindles, nuts, couplings and two pull rods in the H-linkage, or a retainer coupling in the braking force transmitting linkage. Thus, they do not make it possible to overcome the application stroke of the friction brakes by means of a small, isolated auxiliary motor.
German No. 1 240 116 discloses a brake linkage with isolated brake power and auxiliary motor which, at the start of braking, are pressurized through a valve in staggered time and pressure relation to each other, from the same brake pressure line. The linkage branches leading from the respective motors are couplable with one another via an automatic coupling after the brake application stroke has been traversed, so that the auxiliary motor must also accomplish the tight clamping stroke for the friction brake. For automatic adjustment of brake venting play, a special linkage regulator must be provided in the brake linkage, so that the latter becomes complex and expensive.
German No. 811 242 discloses brakes with application and fixed brake cylinders of many different kinds, assuring that the fixed brake cylinder is pressurized during braking only after application of the brake, and that venting during release also proceeds according to an appropriate sequence.
It is known, in principle, with respect to vent play regulators in brake linkages, to use radially prestressed helical springs seated on cylinder surfaces and wound at least substantially free of play, as torque transmitting one-way couplings; these springs can be wound from steel wire of rectangular cross-section.
For brake linkages with a brake shaft drive via a turn lever and causing brake clamping by means of a screw or cam drive, it is known, e.g., from German No. b 70 06 455, to couple the turn lever, via a one-way drive blocking in the turn direction to braking and a friction coupling in the form of a clamping ring arranged parallel to the one-way drive, with the brake shaft. A further, stronger friction coupling also in the form of a friction ring is arranged in series with a turn stop with play corresponding to the desired degree of venting between the brake shaft and an element retained against rotation. However, there is no provision for rapid, energy efficient brake application at the start of braking.
For the most part, pressure air cylinders are used as brake power motors and auxiliary motors, but hydraulic, electromagnetic and electromotor devices are also known for this purpose.